Strip steel cutting die stock and method for its manufacture

ABSTRACT

Strip steel cutting die stock, such as that used in clicker dies, and a technique for cold drawing strip stock whereby cutting edges are formed during the cold drawing operation without the necessity for further machining or grinding. This is achieved by a series of annealing, rolling and drawing steps which insure against decarburization while at the same time enable the production of strip stock of such hardness that it can be subsequently shaped into a clicker die section or the like and then quench-hardened.

United States Patent Milhollan et al. 1 Oct. 2, 1973 STRIP STEEL CUTTING DIE STOCK AND 3,053,703 9/1962 Breyer 148/12 METHOD FOR ITS MANUFACTURE 3,076,361 2/1963 Epsteln et al V 3,281,287 10/1966 Edstrom et a1. 1. 1413/12 [75] Inventors: Thomas H.lVI1lh0llan,C0raopol1s; I 1 1 David Pasquale New Brighton Primary Examiner-W. W S'tallard both of Attorney-T. H. Murray et al. [731 Assignee: Precision-Kidd, inc., West Aliquippa, Pa [57] ABSTRACT V H Strip steel cutting die stock, such as that used in clicker [22] led: 1971 dies, and a technique for cold drawing strip stock [2]] A l N 191,036 whereby cutting edges are formed during the cold drawing operation without the necessity for further ma- 7 chining or grinding. This is achieved by a series of an- [52] [1.8. CI. 148/12, 148/12.] Healing lli g and drawing steps which insure against t t decarburization at the Same time enable the p Fleld of Search duction of Strip Stock of such hardness that can be subsequently shaped into a clicker die section or the [56] References C'ted t like and then quench-hardened.

UNITED STATES PATENTS 6 Claims, 4 Drawing Figures 2,893,902 7/1959 Roberts et a1. 148/12 l STRIP STEEL CUTTING DIE STOCK AND METHOD FOR ITS MANUFACTURE BACKGROUND OF THE INVENTION In the past, steel strip cutting die stock of this type has been cold drawn with relatiely blunt cutting edges. This necessitates sharpening of the edges after forming into a die by grinding or machining, an obviously expensive and time-consuming process.

SUMMARY OF THE INVENTION In accordance with the present invention, steel strip cutting die stock is provided in which cutting edges are formed during a cold drawing operation, thereby eliminating the necessity for a subsequent grinding or machining operation to form the cutting edges. This is achieved by carefully controlled rolling, annealing and drawing operations which insure against decarburization of the cutting edge while providing the necessary hardness to enable the strip to be formed into the shape of a die and thereafter heated and quenched.

. All of the steps of the process hereinafter described in detail should be carefully controlled in order to achieve the desirable results of the invention. In general, however, the steps of the process include (1) hot rolling fully conditioned steel billets into rectangular bar stock, (2) spheroidize annealing the billets in a controlled atmosphere to achieve better machinability and a uniform grain structure, (3) cold rolling the annealed stock to form the general cros section of the desired cutting die while taking in the cold rolling procedure at least a 30 percent reduction to cold work the product as much as possible, (4) stress-reief annealing the thusformed cold rolled product in a controlled atmosphere, and (5) cold drawing the annealed strip through a die while taking no greater than'about a 5 percent reduction in any area of the cross section, followed by a final stress relief anneal. This produces a product having a Rockewll B hardness no greater than 90 which can then be formed into a clicker die section or the like and heated and quenched to produce a Rockwell C hardness of about 48 to 51 and having a cutting edge of 0.005 inch maximum radius.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is an end view of one type of strip steel cutting die stock which can be formed in accordance with the teachings of the invention;

FIG. 2 is an end view of another type of strip steel cutting die stock which can be formed in accordance with .the teachings of the invention;

FIG. 3 is a perspective view of a typical clicker die formed from the stock of FIG. 1, for example; and

FIG. 4 is an enlarged cross-sectional view showing the cutting edge formed in the cold drawing step of the invention.

With reference now to the drawings, and particualrly to FIG. 1, the die stock shown comprises a strip or ribbon of steel having a central portion 10 with flat side walls 12. lntersecting the flat side wall portions 12 are converging side wall portions 14 which terminate in cutting edges 16. The steel cutting die stock of FIG. 2 is similar to that of FIG. 1 and again includes an enlarged central portion 18 communicating with converging side wall portions 20 which terminate in cutting edges 22. In this case, however, the central portion 18 is provided with an integral flange 24 into which is milled a slot 26. It will be understood, of course, that sections can be formed with only one cutting edge; however in most cases dual cutting edges are used.

Both of the die sections shown in FIGS. 1 and 2 can be shaped into a clicker die such as that shown in FIG. 3 and identified by the reference numeral 28. The die 28 of FIG. 3 is formed from stock such as that shown in FIG. 1 and is provided with a cross brace 30 which can be welded or otherwise securely fastened to opposite sides of the die. Alternatively, a die can be formed by bending strip stock, such as that shown in FIG. 2, around a core formed from sheet metal, the periphery of which corresponds substantially to the outline of the desireddie configuration. In this case, the die stock is bent around the core such that the edges of the core fit into the slot26. Thereafter, the strip steel cutting stock can be welded or otherwise securely fastened to the core.

As was explained above, it has been common in the past to cold draw sections, such as those shown in FIGS. land 2, and thereafter form the cutting edges 16 and 22 in a grinding or other machining operation. That is, the die stock, as sold to the ultimate user, had blunt edges rather than sharpened edges 16 and 22. After the stock was formed into a clicker die such as that shown in FIG. 3, it then became necessary to grind or machine the edges, an expensive and timeconsuming operation. In accordance with the present invention, strip steel die stock is provided having a cutting edge or edges formed thereon during a cold' drawing operation with a maximum radius of 0.005 inch. As shown in FIG. 4, every cutting edge, regardless of how sharp it might be, defines a radius when viewed under a microscope, this radius being identified by the reference numeral 32 in FIG.4. The present invention provides a means whereby the radius 32 of the cutting edge is no greater than 0.005 inch maximum, which is well within the sharpness required for clicker die operations.

In practicing the invention, the strip steel cutting die stock is preferably formed from a modified AISI 4150 steel having the follwing broad and preferred ranges of composition:

Broad Preferred Carbon 0 53-058 0.55 Manganese 0.80-0.90 0.85 Silicon 0.20-0.30 0.25 Chromium 0 -070 0.65 Nickel 0 45-055 0.50 Molybdenum 0 15-025 0.20 Iron Bal. Bal.

Billets formed from this steel are initially fully conditioned by grinding to remove all defects so as to prevent any decarburization at the surface of the formed product. This is followed by controlled heating before hot rolling into bar stock. Following hot rolling, the product is pickled in sulfuric acid and thereafter subjected to a spheroidizing anneal in a controlled atmosphere, preferably nitrogen, to prevent any decarburization of the steel. The purpose of the spheroidizing anneal is to soften the product and achieve a uniform grain structure throughout. In the spheroidize annealing process, the product is heated to l,lF and held at this temperature until the dew point is reached. Thereafter, it is heated to l,380F and maintained at this temperature for hours, followed by cooling at 20F per hour to 1,200F, and then air cooled.

Following the spheroidizing anneal, the product is pointed preparatory to a succeeding cold rolling operation and again pickled in sulfuric acid. It is then rinsed, coated with zinc phosphate, again rinsed, and then dipped in lime and a liquid soap.

The product is now ready for cold rolling to form the general cross section of the die stock, such as that shown in FlG. l or FIG. 2. During the cold rolling operation, it is necessary to achieve at least a 30 percent reduction. That is, it is necessary to cold work the product as much as possible, which results in a refined grain structure during subsequent annealing steps. Following cold rolling, the prouct is again annealed in a nitrogen atmosphere by heating to l,100F and holding for the dew point. Thereafter, the product, in coiled form, is heated to l,300F and held at this temperature for 4 hours, followed by cooling at 40F per hour to 1,200F and air cooled. The strip is then pointed and subjected to the same cleaning and lubricating procedures which followed hot rolling.

The product is then drawn through a die, preferably in a bullblock arrangement, and straightened. During the drawing operation, it is essential that not over 5 percent reduction is taken at any cross-sectional area portion of the stock to prevent work hardening. Additionally, it is necessary to provide a drawing die in which the complementary approach angles for any cros-sectional area of the stock are proportional to the amount of reduction taken in that cross-sectional area. That is, the greater the reduction, the greater the complementary approach angles which, of course, are the greatest at the cutting edges 16 and 22 shown in FIGS. 1 and 2.

Finally, after cold drawing, the product is submitted to a stress relief anneal where it is first heated to 1,100F and held for the dew point, followed by heating to 1,340F where the temperature is maintained at this point for 4 hours. After the 4-hour period, the product is cooled at 40F per hour to l,200F and then air cooled.

The resulting strip steel die stock, which now has a Rockwell B hardness no greater than 90, is now ready 5 to be supplied to the user who forms it into a clicker die, for example, such as that shown in FIG. 3. After the clicker die is thus formed and the ends of the strip steel stock joined, it is heated and then water quenched, whereupon it achieves a Rockwell C hardness in the range of about 48 to 51. At the same time, the cutting edge has a radius no greater than 0.005 inch as explained above.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes can be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In the process for forming strip steel cutting die stock, the steps of hot rolling a fully conditioned steel billet into a rectangle, spheroidize annealing the billet in a controlled atmosphere to achieve better machinability and uniform grain structure, cold rolling the annealed stock to form the general cross section of the die stock, stress annealing the thus-formed cold rolled product in a controlled atmosphere, and thereafter cold drawing the annealed strip through a die while forming on the strip during the cold drawing operation at least one cutting edge having a radius no greater than about 0.005 inch.

2. The process of claim 1 wherein at least a 30 percent reduction is taken during the step of cold rolling the annealed stock.

3. The process of claim 2 wherein no greater than a 5 percent reduction is taken during th cold drawing step.

4. The process of claim 1 including the step of annealing the cold drawn strip.

5. The process of claim 4 wherein the annealing steps are carried out in a nonoxidizing atmosphere, the first anneal being carried out at l,380F with controlled cooling, the second anneal being carried out at 1,300F with controlled cooling, and the third annealing step being carried out at 1,340F with controlled cooling.

6. The process of claim 1 wherein the reduction taken at any cross-sectional area of the strip during cold drawing is proportional to the size of that crosssectional area. 5 

2. The process of claim 1 wherein at least a 30 percent reduction is taken during the step of cold rolling the annealed stock.
 3. The process of claim 2 wherein no greater than a 5 percent reduction is taken during th cold drawing step.
 4. The process of claim 1 including the step of annealing the cold drawn strip.
 5. The process of claim 4 wherein the annealing steps are carried out in a nonoxidizing atmosphere, the first anneal being carried out at 1,380*F with controlled cooling, the second anneal being carried out at 1,300*F with controlled cooling, and the third annealing step being carried out at 1,340*F with controlled cooling.
 6. The process of claim 1 wherein the reduction taken at any cross-sectional area of the strip during cold drawing is proportional to the size of that cross-sectional area. 